The overall goal of this project is to prospectively and systematically ascertain the effects of intravenous urography on the cardiovascular system in man. Accordingly, this study is designed to analyze three clinical problems. A. Is the patient with cardiac disease at greater risk than those without heart disease during urography? B. Is there a difference in the frequency and severity of cardiac arrhythmias and ischemic events, as determined by electrocardiographic (EKG) and blood pressure monitoring that is related to the volume of contrast medium administered (50cc standard dose vs. 150cc high dose infusion)? C. Do the currently available contrast media (meglumine diatrizoate, sodium diatrizoate, meglumine iothalamate) exert any differential effects on the incidence and type of adverse cardiac reactions? This protocol will evaluate 384 patients referred for clinically indicated urography. Determination of cardiac status (4 groups), age (2 groups), and dose media (2 groups) will categorize patients for subsequent randomization as to type of contrast media (3 groups) administered. This will result in four patients within each statistical cell block. Following EKG interpretation the data base will be evaluated by several methods of statistical analysis.